The article offers a study of the oldest building of Iecava manor - a stone barn, that has survived after the devastating wars of the 20th century. The history and architecture of the construction of the barn until 2020 seemed to be known. The stone building has a weather cock with the year 1797, and the construction time of the building is related to it. The architectural composition of the main façade and some carefully designed details allowed to hypothesize that the architect of the Duke of Courland - S. Jensen is the author of the building. There is a well-built spacious basement under the building. This indicates the special function of this farm building. A building research study in 2021 found that in the second half of the 18th century, a wooden farmhouse with a basement (or on an existing basement) was built, having a gable roof with pitched ends and timber framed gables. The main façade had a roof overhang, and perhaps this façade was painted red, imitating a brick wall with grey seams. The current appearance of the stone barn was obtained after the exterior walls of the wooden building were replaced by masonry walls. It happened in the first decades of the 19th century. The building was transformed into a masonry structure, leaving the floor beams, ceiling beams, pediments and roof structure of the old wooden building, and expanded by moving the main façade wall ~ 1 m further apart. The function of a wooden building is not clear. Previous hypotheses about a malt in the 18th century are neither denied nor confirmed. The assumption that the brewery was the only brick building in the 1786 inventory is erroneous, as the building was originally made of wood. Presumably, at the beginning of the 19th century, the archaic wooden house with the stone basement had served its time and, being very close to the count's dwelling house, did not meet the highest quality standards for the architecture of the new manor center. The representative character of the building was determined by the late classicist style. Usually old wooden buildings are demolished, but in the case of Iecava, an exception was made. The old wooden building has been partially preserved by transforming it into a new quality building, with better fire safety, spatially wider and more artistically expressive, in accordance with the style of that time. Today, the barn is the oldest existing building in Iecava manor . This study is an example of the importance of structural thinking and knowledge of structures in architectural research. This knowledge is provided by architecture education that is different from formal analysis practiced in the art sciences.